Respirator apparatus and method

ABSTRACT

A fluidically-operated respirator comprises an apneic event circuit (10) and a demand gas circuit (20). The apneic event circuit (10) comprises a variable capacitance device (132) and an exhaust means (130) which rapidly discharge fluid from the circuit (10) when an inspiration occurs. If an apneic event occurs, the circuit (10) activates one or more signals (136) as a predetermined volume of fluid is built up in the circuit (10). The demand gas circuit (20) of the respirator supplies respirating gas to a patient at the beginning of an inspiration and for a time period which is a fraction of the duration of the inspiration.

This is a continuation, of application Ser. No. 210,654, filed Nov. 26,1980 and now U.S. Pat. No. 4,457,303.

BACKGROUND

This invention pertains to respirator apparatus and methods foroperating the same, and particularly to such apparatus and operatingmethods which feature intermittent demand oxygen flow and/or apneicevent detection.

Intermittent demand oxygen flow has been tried in the past as an attemptto reduce high costs generally involved in supplying oxygen flow to apatient. D. Auerbach et al. (Chest, 74: 1 July 1978, pp. 39-44) brieflyreview the history of such attempts and report test results observedwith an oxygen cannula system using intermittent-demand nasal flow. Thedevice reported by Auerbach et al. uses a spring-loaded diaphragm inconjunction with a cannula to sense, in two distinct modes, either thenegative pressure created by inspiration or the positive pressurecreated by expiration. In a negative mode the reported device suppliesoxygen to the patient as long as negative pressure is detected; in thepositive mode oxygen is supplied as long as a positive pressure is notdetected.

Fluidic logic elements have also been used in intermittent demand oxygensystems to sense negative and positive pressures created by inspirationand expiration. In this regard, U.S. Pat. No. 3,976,065 to Durkandiscusses prior art ventilators employing fluidic elements and furtherdiscloses a digital fluidic ventilator wherein a single fluidicflip-flop serves as a primary control element and wherein any one of aplurality of operating modes is obtained by adjusting a bias signalapplied to the flip-flop.

Prior art intermittent demand oxygen devices, whether sensing negativeor positive pressure, supply oxygen to a patient substantiallythroughout the duration of an inspiration. If a given patient were tobreathe at the rate of 10 breaths per minute, for example, each breathwould average 6 seconds. For such a patient, an inspiration wouldnormally be sensed for about 2 seconds of the 6 seconds per breath; anexpiration would normally be sensed for the four remaining seconds.Prior art devices, therefore, would supply oxygen for the full durationof inspiration--in this case, 2 seconds.

In some existing devices, such as that tested by Auerbach et al., supra,the oxygen supplied for the full duration of inspiration tends tocommence with a surge in the pattern of flow. Heretofore this surge hasbeen considered unnecessary and wasteful. In some devices other fluidicelements, such as a flowmeter, for example, have been incorporatedintermediate the patient and the oxygen supply to dampen the surge.

The applicant has clinically observed, however, that in the breathingprocess oxygen is absorbed into the blood essentially only during anearly stage of inspiration. That is, it is during an early stage ofinspiration that oxygen effectively reaches the alveoli. Oxygen appliedduring the latter stages of inspiration remains in "dead spaces" such asthe pharynx, trachea, and bronchial tubes. Hence, the applicant hasobserved and concluded that in operating respirator apparatus it is moreadvantageous to apply a greater volume of oxygen per second and to applythe oxygen only during an effective early stage of inspiration ratherthan to apply a conventional volume per second throughout the durationof inspiration.

For the case described above, the effective early stage may last forapproximately 0.25 seconds. For most cases, the effective early stage isless than approximately one-quarter and usually approximately one-eighthof the duration of the inspiration. Therefore, if oxygen were suppliedat twice the normal volume per second rate (for example: 100 cc/sec.rather than 50 cc/sec.), a savings of more than one-half--and in mostinstances more than three-quarters--would be realized. Present dayintermittent demand oxygen devices are not capable of operating inaccordance with this effective early stage inspiratory phenomenon.

Various prior art respirator apparatus attempt to detect apneic events.Basically, apnea is a breathing disorder that may be caused by cessationof central nervous system output, by upper airway obstruction, or by acombination of the two. This disorder has been implicated in the SuddenInfant Death Syndrome. The condition is also especially hazardous inpatients with chronic obstructive lung disease since dangerous cardiacarrhythmias can occur due to the anoxia.

Of the prior art devices that attempt to detect apneic events, many(including the devices disclosed in U.S. Pat. Nos. 3,357,428 to Carlsonand 4,206,754 to Cox) periodically generate electrical (as opposed tofluidic) signals which are electrically monitored to determine when apatient has ceased to breathe satisfactorily and which activate an alarmas a warning indicator.

Prior art respirators which utilize fluidic signals to detect apneicevents basically employ fixed capacitance reservoirs for either gaugingor controlling the length of time between inspirations. Examples of suchrespirators are seen in U.S. Pat. Nos. 3,910,270 to Stewart; 3,659,598to Peters et al.; and, 4,141,354 to Ismach. In apneic event detectorsusing fluidic signals, however, fixed volume capacitances are inadequatesince fluid compression in a fixed volume is not compatible with the lowpressures often used in a fluidic logic circuit. Moreover, the prior artfixed volume capacitances exhaust through fluidic logic devicesthemselves and at a rate much slower than what is desirable in anefficient apneic detector.

In view of the above, an object of this invention is to provide arespirator apparatus and method of operating the same whereinrespirating gas is supplied to a patient substantially at the beginningof an inspiration and for a time period thereafter which is a fractionof the duration of inspiration.

An advantage of this invention is the provision of an economical andefficient respirator apparatus allowing the conservation of arespirating gas, such as oxygen.

Another object of this invention is to provide a respirator apparatushaving an fluidically-operated apneic event detector.

A further advantage of this invention is the provision of a respiratorapparatus having an apneic event detector with a variable volumecapacitance compatible with fluidic logic elements and means for rapidexhaust thereof.

SUMMARY

A respirator apparatus includes means for sensing either an inspirationor an expiration of a patient and first generating means for generatingat either a first or a second output port a first fluid signalindicative of the duration of the inspiration or expiration. The firstoutput port of the first generating means is connected to afluidically-operated apneic event circuit which includes a variablevolume capacitance device (such as an elastomeric balloon) operating inconjunction with an exhaust valve. The apneic event circuit selectivelyactivates one or more signaling means (such as a counter, an alarm, oran ECG monitor) when a patient has not inspired within a predeterminedtime.

A second output port of the first generating means is connected to afluidically-operated demand gas controller circuit. In its variousembodiments the demand gas controller circuit includes second generatingmeans responsive to the first fluid signal for generating a second fluidsignal having a duration related to the duration of the first fluidsignal by a pre-determined relationship. The demand oxygen controllercircuit further includes source means including valve means responsiveto the second fluid signal for controlling the application of arespirating gas to a patient for a time period relative to the durationof the second fluid signal. Preferably the duration of application ofthe respirating gas to the patient is less than 0.25 of the duration ofan inspiration.

Laminar proportional amplifiers are used as sensing means to sense verysmall pressures, such as those created by initial attempts to inspireand expire.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention.

FIG. 1 is a schematic diagram of a respirator apparatus according to oneembodiment of the invention;

FIG. 2 is a schematic diagram illustrating a sensing means suitable foruse in the invention;

FIGS. 3A, 3B, and 3C are schematic diagrams illustrating differingalternate embodiments of first generating means suitable for use in theinvention;

FIG. 4 is a schematic diagram illustrating a demand controller circuitaccording to an embodiment of the invention; and,

FIGS. 5A, 5B and 5C are graphs illustrating various differing manners ofsupplying a respirating gas to a patient.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a respirator apparatus according to one embodiment ofthe invention which includes an apneic event circuit 10 and a demand gascontroller circuit 20. The embodiment of FIG. 1 further includes a nasalcannula, or nasal prongs 22, connected by a sensing line 24 to a sensingmeans 26. When there is a nasal blockage, such as by polyps, forinstance, a mask can be used instead of nasal prongs 22. For purpose ofbrevity, any fluid conveying means, such as a duct, pipe, channel, orother closed fluid conduit is hereinafter referred to as a line.

Sensing means 26 is a device capable of sensing the direction andduration of pressure flow in a patient's respiratory system. That is,sensing means 26 is capable of detecting negative pressure created by apatient's attempt to inspire and positive pressure created by anexpiration. As generally shown in FIG. 1, sensing means 26 includes afirst control port 28 connected to sensing line 24; a second controlport 30 fluidically connected to bias control valve 32; a power streamport 34 connected by a line 38 to a fluid source 36; and, two outputports, or output legs, 40 and 42.

The fluid source 36 shown connected to sensing means 26 in FIG. 1 may bea small pump or conventional wall supply device for providing air,oxygen, or other desired fluid to the respirator apparatus. While theembodiments hereinafter described employ fluidic elements connected toone of a plurality of fluid sources 46 (each source 46 basicallyresembling fluid source 36), it should be understood that the fluidicelements may be instead connected by suitable connectors to a singlesource, such as source 36. When desired, a restrictive device 48, suchas a variable restrictor or a pressure regulator, may be connectedintermediate any source and a fluidic element.

As seen in FIG. 2, one embodiment of sensing means 26 suitably comprisesa plurality of fluid amplifier devices. In particular, the embodiment ofFIG. 2 includes a three stage amplifier network comprising fluidamplifiers 50, 52, and 54. It should be understood, however, that otherembodiments of sensing means 26 may have any suitable number of stagesdepending on the degree of amplification desired. The fluid amplifierseach have first control ports (denoted as 50a, 52a, and 54a,respectively); second control ports (50b, 52b, 54b, respectively); powerstream ports (50c, 52c, 54c, respectively); first output ports (50d,52d, 54d, respectively); and, second output ports (50e, 52e, 54e,respectively).

The amplifiers 50, 52, and 54 are connected in a three stageconfiguration in the following manner: output port 50d is connected tocontrol port 52b by line 56; output port 50e is connected to controlport 52a by line 58; output port 52d is connected to control port 54c bya line 60; and, output port 52e is connected to control port 54a by aline 62. Each power stream input port is connected to a fluid source:port 52c and 54c are connected to the source 46 while port 50c isconnected to the source 36 via line 34. As seen in FIG. 2, control port50a is connected to the sensing line 24; control port 50b is essentiallythe second control port 30 of sensing means 26; output port 54d isconnected to output leg 40 of sensing means 26; and, output port 54e isconnected to output leg 42 of sensing means 26.

The amplifiers 50, 52, and 54 of the FIG. 2 embodiment of sensing means26 are connected so that there is a 6:1 gain in each stage ofamplification. The amplifiers 50, 52, and 54 of FIG. 2 may either beconventional fluid flow fluidic amplifiers operated at a sufficientlylow pressure that the flow becomes laminar or laminar flow fluidicamplifiers. Laminar flow fluidic amplifiers are highly sensitive and uselaminar flow rather than turbulent flow as in typical Coanda typedevices. The laminar flow fluidic amplifiers of this type are availablethrough Tritech, Inc. of Columbia, Maryland. In either case, the sensingmeans 26 is generally capable of sensing a first instance of inspirationwith a negative pressure of approximately 0.5 millimeters of water.

The respirator apparatus of FIG. 1 further comprises first generatingmeans 64 which includes a first control port 66, a second control port68, a first output port or leg 70, and a second output port or leg 72.

FIG. 3A illustrates in more detail an embodiment of generating meanssuitable for use with the invention. Generating means 64A of FIG. 3Acomprises a fluidic amplifier 74 and a NOR gate 76. The amplifier 74comprises a first control port 74a; a second control port 74b; a powerstream port 74c; a first output port 74d; and, a second output 74e. Inthe FIG. 3A embodiment control ports 74a and 74b are essentially controlports 68 and 66, respectively, of first generating means 64A; powerstream port 74c is connected to the source 46; and, output port 74e isvented to atmosphere. NOR gate 76 comprises a control port 76a; a powerstream port 76c; a first output port 76d; and, a second output port 76e.From FIG. 3 it should be understood that power stream 76c is connectedto the source 46 and that output ports 76d and 76e are connected to theoutput legs 70 and 72, respectively, of first generating means 64. NORgate 76 is connected to amplifier 74 by a line 78 which connects outputport 74d to control port 76a.

FIG. 3B illustrates a second embodiment of a first generating meanssuitable for use with the invention. In particular, FIG. 3B illustratesa first generating means 64B which comprises a laminar proportionalfluidic amplifier 79 and a fluidic laminar proportional flip-flop 80.The fluidic flip-flop 80 further comprises two laminar proportionalamplifiers 81 and 82. Each of the amplifiers 79, 81, and 82 have inputports, power stream ports, and output ports labeled in the alphabeticalconvention established by the amplifiers 50, 52, 54, and 74 discussedabove. Likewise, each amplifier has its power stream input connected tothe sources 46.

Amplifier 81 of flip-flop 80 is connected to the amplifier 79 by lines83 and 84--Line 83 connects control port 81b to output port 79d and line84 connects control port 81a to output port 79e. The amplifiers 81 and82 of flip-flop 80 are interconnected by lines 85 and 86 and by twofeedback paths hereinafter described. Line 85 connects output port 81dto control port 82b and line 86 connects output port 81e to control port82a. Feedback path 87a interconnects output port 81e and input port 81bof amplifier 81 and feedback path 87b interconnects output port 81d andinput port 81a of amplifier 81. Control input ports 79a and 79b areessentially control ports 68 and 66, respectively, of first generatingmeans 64B and output ports 82d and 82e connect to output legs 70 and 72,respectively. Various resistances, generally denoted as 88, arepositioned at various points in the flip-flop 80, including on thefeedback paths 87 a and 87b.

FIG. 3C illustrates a third embodiment of a first generating means alsosuitable for use with the invention. In particular, FIG. 3C illustratesa first generating means 64C which comprises a proportional fluidicamplifier 90 and a bistable fluidic flip-flop 92. Amplifier 90 andflip-flop 92 have input ports, power stream ports, and output portslabeled in the alphabetical convention mentioned above. Flip-flop 92 isconnected to the amplifier 90 by lines 93 and 94--line 93 connectscontrol port 92b to output port 90d and line 94 connects control port92a to output port 90c. Control ports 90a and 90b are essentiallycontrol ports 68 and 66, respectively, of first generating means 64c andoutput ports 92d and 92e connected to output legs 72 and 70,respectively. The output port 90e of amplifier 90 is geometricallybiased so that when either no signal is applied to the amplifier 90, orwhen a signal is applied to input port 90b thereof, a fluidic signalresults on leg 72 of the generating means 64c. A first generating meansresembling the means illustrated as means 64c in FIG. 3C is a SensorTrigger (code 192681) developed by Corning Glass Works.

FIG. 1 illustrates one embodiment of a demand gas controller circuit 20.The demand gas controller circuit 20 includes a second generating means96 and a source means 98.

The second generating means 96 of demand gas controller circuit 20comprises a first output port 96a vented to atmosphere; a second outputport 96b connected via line 100 to the source means 98; a first inputport 96c connected to the source 46; and, a second input port 96connected by a line 102 to the output leg 70 of first generating means64. Second generating means 96 further comprises a substantiallyclosed-loop fluidic path 104 which has a first end 104a perpendicularlyintersecting the input port 96c on one side thereof and a second end104b perpendicularly intersecting the input port 96c on a second sidethereof. The ends 104a and 104b are essentially linear at the point ofintersection with input port 96c. The fluidic path 104 has thereon oneor more timing means, such as a fluid restrictive device 106 and/or acapacitance device 108. As shown in the embodiment of FIG. 1, therestrictive device 106 is a variable resistor and the capacitance 108 isa variable capacitance, such as an elastomeric balloon. The restrictivedevice 106 and capacitance 108 may be interchanged with similarrestrictive devices or capacitances having different values andcapacitances.

Source means 98 of the demand gas controller circuit 20 includes ademand valve 110 connected to a source of respirating gas 112 by a line114. Intermediate the demand valve 110 and source 112 on line 114 are aregulator 116 and a flowmeter 118. The demand valve 110 is alsoconnected to a fluid conveying means, or line 120, for supplying therespirating gas to the nasal prongs 22. A bypass line 122 with a bypassswitch 124 thereon is connected between lines 114 and 120 forselectively short-circuiting the demand valve 110. In the above regard,the demand valve 110 may be of any suitable fabrication, such as amoving part valve or a diaphragm valve. An ALCON Series A Model 7986valve has been preferred in practice.

A second embodiment of a suitable demand gas controller circuit isillustrated in FIG. 4. This controller circuit 20' includes a secondgenerating means 96' and a source means 98'. The second generating means96' comprises a first output port 96a' connected via line 100' to thesource means 98'; a second output port 96b' vented to atmosphere; afirst input port 96c' connected to the source 46; and, a second inputport 96d' connected by a line 102' to the output leg 70 of the firstgenerating means 64. Like the embodiment of FIG. 1, second generatingmeans 96' includes a fluidic path 104 with respective ends 104a' and104b' and timing means 106' and 108'.

Source means 98' comprises a diaphragm valve 110' connected to asuitable source 112' by a line 114' much in the manner of FIG. 1. Demandvalve 110' has a first input port 110a' connected by line 100' to thesecond generating means 96'; a second input port 110b' connected to theline 114'; an output port 110c' connected to the fluid conveying means120; and, a flexible diaphragm 110d. In like manner as the FIG. 1embodiment, the embodiment of FIG. 4 also includes a bypass line 122'having a bypass switch 124' thereon.

In either of the embodiments of FIG. 1 or FIG. 4, the demand gascontroller circuit may further comprise a counter and display circuitlabeled as 160 in FIG. 1 and 160' in FIG. 4. The circuit 160 of FIG. 1includes a pneumatic counter 162 connected by a line 164 to line 100.The circuit 160' of FIG. 4 includes a similar pneumatic counter 162'connected by a line 164' to second output port 96b' of second generatingmeans 96'.

At this point, the ensuing discussion of the structure of the FIG. 1embodiment of the counter and display circuit 160 with its unprimedreference numbers is applicable as well to the embodiment of FIG. 4 withits corresponding but unprimed reference numbers, so that the twofigures need not be discussed separately. The circuit 160 furtherincludes two pressure electric devices 166 and 168 suitable forgenerating an electrical signal having a duration equal to the durationof a fluidic signal applied as an input thereto. Device 166 ispneumatically connected on line 170 to line 120 and device 168 ispneumatically connected on line 172 to line 102. The device 166 iselectrically connected by a wire 174 to a display device 176; device 168is electrically connected by a wire 178 to a display device 180. Thedisplay devices 176 and 180 each include unillustrated components suchas clocking means, reset means, and a readout means (such as a digitalreadout).

In either of the embodiments of FIG. 1 or FIG. 4, an oscillator 126 maybe connected on line 120 between the patient (nasal prongs 22) and thesource means (110 or 110'). The oscillator 126 is employed to createhigh frequency oscillations in the flow of the respirating gas whichincreases diffusion of the gas into the lungs. The oscillator 126 maycomprise, for example, a rotary motor or a pump. A bypass line 127 witha switch 128 thereon has both its extremities connected to line 120 buton opposing sides of the oscillator 126. Selective activation of theswitch 128 effectively short circuits the oscillator 126 and providesfor a non-oscillatory flow of respirating gas.

The apneic event circuit 10 is fluidically connected to the output leg72 of the first generating means 64 and includes an exhaust means 130(such as a mushroom valve); a variable capacitance device 132 (such asan elastomeric balloon); a digital fluidic device 134 (such as a NORgate); and, at least one signaling means (such as any of the following:a pneumatically operated digital counter 136a; an alarm 136b; and, anelectrocardiogram (ECG) monitor 136c).

The variable capacitance device 132 and NOR gate 134 of the apneic eventcircuit 10 are connected to the output leg 72 of the first generatingmeans 64 by a line 138. A fluid resistor 140 is interposed on line 138between the first generating means 64 and the variable capacitancedevice 132. A fluid path or line 142 is connected in parallel to line138 around the fluid resistor 140. The mushroom exhaust valve 130 lieson path 142 and is adapted to close when a fluid signal is appliedthereon from the direction of generating means 64.

NOR gate 134 comprises a first input port 134a connected to the supply46; a second input port 134b connected to the line 138; a first outputport 134c vented to atmosphere; and, a second output port 134d connectedto the signaling means. In this regard, the output port 134d isconnected by a line 144 to a pressure electric switch 146 and by lines144 and 148 to the counter 136a. The pressure electric switch 146 iselectrically connected by suitable wires 148 and 150 to the alarm means136b and the electrocardiogram monitor 136c. The alarm means 136b may beeither an audible alarm, a visual alarm, or both.

A pressure/electric device 152 is pneumatically connected by a line 154to a portion of line 138 which is intermediate the first generatingmeans 64 and the fluid restrictor 140. The pressure electric device 152is a type which generates an electrical signal having a duration equalto the duration of a fluidic signal applied as an input thereto. Thepressure electric device 152 is electrically connected by a wire 156 toa display device 158. The display device 158 is of a type mentionedearlier with reference to devices 176 and 180.

Before discussing the operation of the abovedescribed respiratorapparatus, it should be recalled that the applicant has clinicallyobserved in the breathing process that oxygen is absorbed into the bloodessentially only during an early stage of inspiration. To illustratethis observation, reference is now made to FIGS. 5A, 5B, and 5C. Forpurposes of discussion, when a patient breathes at the rate of 10breaths per minute, each breath averages approximately 6 seconds. Toillustrate this example, each of the graphs of FIGS. 5A through 5C havea time axis incremented in seconds (sec) ranging from 0 to 6 seconds.For simplicity, a second axis of the graph is incremented from 0 to 6liters per minute (L/Min) to indicate the rate of supply of respiratinggas to a patient.

FIG. 5A illustrates a device which continuously supplies respirating gasto a patient. The graph of FIG. 5A shows an essentially straighthorizontal line, the area under the line basically corresponding to theamount of gas supplied. For the 6 second time period shown, the gassupplied approximates 0.3 L=3 L/MIN×1 MIN/60 SEC×6 SEC. Inasmuch as onlyabout 2 seconds of a 6 second breath are required for inspiration, aconsiderable waste occurs in using the continuous supply device of FIG.5A.

The more economical prior art intermittent demand devices were devisedto supply the respirating gas only during inspiration. Such devices arerepresented by the graph of FIG. 5B, which shows an essentially straighthorizontal line lasting for 2 seconds (the approximate length of anentire inspiration). The gas supplied in FIG. 5B approximates 0.1L.

As noted above, the applicant has observed that in operating respiratorapparatus it is more advantageous to apply a greater volume ofrespirating gas per minute at an effective early stage of inspirationrather than a conventional volume per minute rate throughout theduration of inspiration. Hence, FIG. 5C illustrates the applicant'sfinding that it is preferable to provide the greater volume of oxygenper minute at an early stage of inspiration. This effective early stageis less than approximately one-quarter (and usually approximatelyone-eighth) of the duration of the inspiration. In particular, FIG. 5Cillustrates a "spike" S of oxygen flow of approximately 6 L/Min lastingfor approximately 0.25 sec. Hence, the gas supplied in FIG. 5Capproximates less than 0.025 L=6 L/MIN×1 MIN/60 SEC×0.25 SEC. Thestructure described above and operated in the manner describedhereinafter facilitate the supply of a respirating gas, such as oxygento a patient, in accordance with the manner depicted in FIG. 5C.

When a patient attempts to inhale, a negative pressure created in thenasal prongs 22 and line 24 is sensed by the sensing means 26. Asdescribed hereinbefore, the sensing means 26 is capable of detecting anegative pressure as small as 0.5 millimeters of water. Upon sensing anegative pressure created by inspiration, the sensing means 26 generatesa fluid signal on output leg 42.

In the above regard, and with reference to the embodiment of the sensingmeans 26 illustrated in FIG. 2, negative pressure on sensing line 24causes the power stream applied at port 34 of the sensing means 26 todeflect to output port 50e. The resultant fluid signal is applied alongline 58 to the control port 52a of amplifier 52. As a result, the powerstream entering port 52c of amplifier 52 is deflected to output port 52dand creates a signal on line 60. In like manner, the signal on line 60is applied to control port 54c of an amplifier 54 and results in a fluidsignal being created on output leg 42 of the sensing means 26. For theembodiment shown, each stage of amplifiers in the sensing means 26achieves approximately a 6:1 gain in amplification.

The fluid signal on output leg 42 of sensing means 26 is applied to thecontrol port 68 of first generating means 64 and, as describedhereinafter with respect to each alternate embodiment of means 64,ultimately results in a first fluid signal being generated and appliedto output leg 70. This first fluid signal has a duration substantiallyequalling the duration of the patient's inspiration.

In the generating means 64A of the embodiment depicted in FIG. 3A, thesignal on output leg 42 is applied to the control port 74a of amplifier74 and deflects the power stream applied at port 74c to the output port74d, thereby creating a fluid signal on line 78. The fluid signal online 78 is applied to the control port 76a of NOR gate 76 and deflectsthe power stream entering at port 76c to the output 76d, therebycreating the first fluid signal signal on output leg 70.

In the generating means 64B of the embodiment depicted in FIG. 3B, thesignal on output leg 42 is applied to the control port 79a of amplifier79 for deflecting the power stream entering at input port 79c to theoutput port 79d, thereby creating a fluid signal on line 83. The fluidsignal on line 83 is applied to the flip-flop 80 and particularly to theamplifier 81 at control port 81b. The fluid signal on line 83 deflectsthe power stream entering port 81c toward output port 81e, therebycreating a fluid signal both on line 86 and feedback line 87a. Thesignal on line 86 is applied to control port 82a of amplifier 82 fordeflecting the power stream entering port 82c toward the output port82e, thereby generating the first fluid signal on output leg 70.

In the generating means 64C of the embodiment depicted in FIG. 3C, thesignal on output leg 42 applied to control port 90a of amplifier 90overcomes the geometrical bias and deflect the power stream enteringport 90c to the output port 90d, thereby creating a fluid signal on line93. The signal on line 93 is applied to control port 92b of bistableflip-flop 92 and, in a similar manner, deflects the power streamentering at port 92c to the output port 92b, thereby generating thefirst fluid signal on output leg 70.

The discussion of the operation of the inspiration phase of therespirator apparatus is now bifurcated to take into consideration thetwo differing embodiments of the demand gas controller circuits 20 and20' of FIG. 1 and FIG. 4, respectively.

With reference to the demand gas controller circuit 20 of FIG. 1, thefirst fluid signal generated by means 64 on output leg 70 is applied tothe second generating means 96 on line 102. It should be evident fromFIG. 1 that, absent a fluid signal on line 102, the power streamentering at port 96c of the generating means 96 is vented to atmospherethrough output port 96a. However, when the first fluid signal is appliedon line 102 to the second generating means 96, the power stream enteringat port 96c is deflected to the output port 96b for a period of time inthe manner hereinafter described.

Upon application of the first fluid signal on line 102 to the port 96dof second generating means 96, the power stream entering port 96c isdeflected from the output port 96a to the output port 96b, therebycreating a second fluid signal on line 100 which is applied to thesource means 98. The first fluid signal on line 102 is also applied tothe fluidic path 104 which has thereon timing means (such as theresistance 106 and the capacitance device 108). The timing means delaysthe passage of the first fluid signal around the closed loop fluidicpath 104 for a pre-determined time. That is, an appropriate value ischosen for the resistance of the variable resistor 106 and a capacitancedevice 108 of appropriate maximum capacity is chosen so that the firstfluid signal travelling around the closed loop fluidic circuit 104 willbe delayed for a pre-determined time before the signal reaches thesecond end 104b of the fluidic circuit 104. When the first fluid signaltravelling around the closed loop fluidic path 104 reaches the secondend 104b, the fluidic pressure on each side of the power stream enteringat port 96c is equalized so that the power stream is no longer deflectedout the port 96b but instead is again vented to atmosphere through theport 96a.

Thus, the second generating means 96 generates a second fluid signal online 100, the second fluid signal having a duration related to theduration of the first fluid signal applied from output leg 70 on line102. The duration of the first fluid signal on line 102 and the secondfluid signal on line 100 are in a pre-determined relationship which isdependent upon the values and sizes chosen for the timing meanscomprising second generating means 96. Such values and sizes should bechosen for this embodiment such that the ratio of the duration of saidsecond fluid signal to the duration of said first fluid signal, andhence the duration of the inspiration, is less than 0.25. In many casesthe ratio may approximate 0.125, if desired.

The valve means 110 of source means 98 receives a supply of respiratinggas from the source 112 along line 114. Valve means 110 provides the gasto the patient on line 120 for a time period corresponding to theduration of the second fluid signal as received on line 100. Hence,according to the pre-determined relationships given above, the sourcemeans 98 supplies respiration gas to the patient for less than 0.5seconds after the first instance of inspiration.

With reference to the demand gas controller 20' of the embodiment ofFIG. 4, the first fluid signal on output leg 70 of generating means 64is applied on line 102' to the second generating means 96' much in themanner as with the embodiment of FIG. 1. However, it should be notedthat absent such a signal the power stream entering at port 96c' is notvented to atmosphere but travels to the output port 96a' as a secondfluid signal on line 100'. Upon application of the first fluid signal online 102' to input port 96d' of the second generating means 96', thepower stream entering port 96c' is deflected from the output port 96a'to the output port 96b' where it is vented to atmosphere for a timesubstantially equivalent to the time required for the first fluid signalto travel around the closed-loop fluidic path 104' and thereafterequalize fluid pressure on both sides of the power stream.

In the above respect, the fluid path 104' resembles the fluid path 104of the FIG. 1 embodiment and includes similar timing means such asresistor 106' and capacitance 108'. In the embodiment of FIG. 4, thevalues and sizes of the timing means are chosen such that the ratio ofthe duration of the second fluid signal applied on line 100' to theduration of the first fluid signal received on line 102' is greater than0.75 and, in some cases, is greater than 0.875. Of course, the secondfluid signal is applied on line 100' only during the latter part ofinspiration so that the power stream entering port 96c' is vented toatmosphere through port 96b' substantially at the first instance ofinspiration and for a short time period thereafter.

The valve means 110' of source means 98' receives a supply ofrespirating gas on line 114' from a source 112' and, in the absence ofthe second fluid signal on line 100', supplies the respirating gas tothe the patient on line 120. In this regard, while the presence of thesecond fluid signal on line 100' biases the diaphram 110d' against therespirating gas input port 110b', the absence of the second fluid signalon line 100' allows the pressure created on line 114' at input port 110bto deflect the diaphragm 110d' and allow passage of the respirating gasthrough the valve means 110' and out the output port 110c'. Hence, inaccordance with the predetermined timing relationship discussed abovefor the embodiment of FIG. 4, the valve means 110' supplies respiratinggas to the patient after a first instance of inspiration for less than0.5 seconds.

The counter and display circuits 160 and 160' of the respectiveembodiments provide the operator or attending physician with datarelative to the patient's respiratory activity and the operation of thedemand gas controller. The counter 162 of FIG. 1 connected to line 100is incremented whenever a fluid signal is applied to line 100. Thus,counter 162 tabulates the number of inspirations attempted by a patient.The counter 162' of FIG. 4 is connected to second output port 96b' ofsecond generating means 96' and likewise is incremented whenever aninspiration is attempted (whenever the output of means 96' is vented toatmosphere).

Discussing now the further operation of both embodiments of the counterand display circuits 160 and 160' with regard only to the unprimedreference numbers for sake of brevity, the operator or attendingphysician is able to observe on display devices 176 and 180,respectively, the duration of the supply of respirating gas to thepatient on line 120 and the duration of the patient's inspiration asindicated by the fluid signal on line 102. In this regard, the fluidsignals are converted to electrical signals by devices 166 and 168,respectively. The duration of the electrical signals are clocked (ortimed) by the devices 176 and 180. The devices 176 and 180 display onreadout means a numerical value (preferably digital) corresponding tothe duration and are then reset in a conventional manner. The displaydevices 176 and 180 are especially useful as the operator or attendingphysician adjust, calibrates, or selectively interchanges the timingmeans, such as variable resistor 106 and/or capacitor 108, of secondgenerating means 96.

With reference now to both demand gas controller means 20 and 20' of theembodiments of FIG. 1 and FIG. 4, respectively, it should be understoodthat both illustrated controllers can be easily adapted to supplyrespirating gas throughout the duration of inspiration if so desired.This can be accomplished in several ways. For example, the value ofrestrictive device 106 may be chosen so that the resistance is so greaton the path 104 that output occurs at output port 96b throughoutinspiration. Or, as another example, a bypass line (unillustrated) witha switch thereon may selectively short circuit the second generatingmeans 96. In such a mode of operation, the pre-determined relationshipbetween the first and second fluid, signals would be a ratio of 1:1, ora fraction of 1/1.

Again with reference to both demand gas controller means 20 and 20' ofthe embodiments of FIG. 1 and FIG. 4, respectively, the respiratorapparatus can be operated in a continuous mode by closing appropriatebypass switches (124 in FIG. 1 and 124' in FIG. 4) Closing the switch124 (or 124') allows for the continuous flow of the respirating gas fromthe source 112 (or 112') through the lines 114, 122, and 120 (or 114',122', and 120).

With further reference to both embodiments of the demand gas controllersshown in FIGS. 1 and 4, the flowmeter 118 (or 118' in FIG. 4) should beconnected intermediate valve means 110 (or 110') and source 112 (or112') instead of intermediate the valve means 110 (or 110') and thenasal prongs 22. Otherwise, the "spike" S illustrated in FIG. 5C wouldbe dampened, resulting in an insufficient gas supply.

Since during inspiration the generating means 64 applies the first fluidsignal on output leg 70 instead of output leg 72, the apneic eventcircuit 10 does not receive a fluid signal. In fact, during inspirationfluid collected in the variable capacitance device 132 is rapidlydischarged out the mushroom exhalation valve 130 since the valve is notbiased shut by a fluid signal applied on fluid path 142. The variablecapacitance and elastomeric nature of the device 132, operating inconjunction with the mushroom exhaust valve 130, facilitate the quickdischarge of fluid from the variable capacitance device 132. A fixedvolume capacitance could not adequately perform this function and wouldbe incompatible with the low pressures used in the fluidic logic circuitdiscussed herein.

When a patient exhales, a positive pressure is created in the nasalprongs 22 and on the sensing line 24. The sensing means 26 senses thepositive pressure and creates a fluid signal on its output leg 40. Withreference to the embodiment of the sensing means 26 shown in FIG. 2, theapplication of positive pressure at control port 50a of amplifier 50 inmeans 26 causes the power stream entering at port 50e thereof to deflectto output port 50d, thereby-creating a signal on line 56. The signal online 56 is applied to control port 52b of amplifier 52 which, in turn,creates a signal on line 62 for application to control port 54a ofamplifier 54. Amplifier 54 then creates a fluid signal on output leg 40.Although not described in detail at this point, it should be understoodthat the amplifiers 52 and 54 operate in accordance with the sameprinciples as discussed above with regard to the negative pressureoperation phase. Of course, fluid signals are applied to opposite inputports and discharged out opposite output ports than those discussed inthe negative pressure operation phase.

The fluid signal on line 40 is applied to the control port 66 of firstgenerating means 64 and, in the manner herein described with referenceto each of the differing embodiments of FIGS. 3A, 3B, and 3C, generatesa first fluid signal on output leg 72 thereof.

In the generating means 64A of the embodiment illustrated in FIG. 3A,the fluid signal on output leg 40 is applied to control port 74b andcauses the power stream entering control port 74c to be vented toatmosphere through output port 74e. Therefore, no fluid signal istransmitted on line 78 for application to NOR gate 76. The power streamentering port 76c of the NOR gate 76 continues undeflected and isdischarged out the output leg 72.

In the generating means 64B of the embodiment illustrated in FIG. 3B,the signal on output leg 40 is applied to control ports 79b of amplifier79 and deflects the power stream entering port 79c so that a signal iscreated on line 84. The signal on line 84 is applied to the flip-flop 80which ultimately generates a first fluid signal on output leg 72thereof. Although not described in detail at this point, it should againbe understood that the amplifiers 81 and 82 comprising flip-flop 80function in accordance with the same principles discussed above withreference to the negative pressure operating mode. Of course, signals toamplifiers 81 and 82 may be applied at opposing input ports thandiscussed above and output signals discharged from opposing outputports.

In the generating means 64C of the embodiment illustrated in FIG. 3C,the fluid signal on output leg 40 is applied to control port 90b ofamplifier 90 for deflecting the power stream entering port 90c to outputport 90e, thereby creating a signal on line 94. The signal 94 enteringcontrol port 92a of the bi-stable flip-flop 92 causes the power streamentering port 92c to deflect toward output port 92d, thereby generatinga first fluid signal on output leg 72.

In contrasting the three embodiments of the first generating means 64discussed above, it should be noted that the generating means 64B ofFIG. 3B requires an expiration for its output to switch from leg 70 toleg 72. The generating means 64A and 64C, on the other hand,automatically switch their outputs from leg 70 to leg 72 upon thecessation of an inspiration.

Since in the positive pressure operating mode the first generating means64 generates a first fluid signal on output leg 72, no fluid signal isapplied on output leg 70 to the demand gas controller circuit. Asdiscussed separately above with reference to the respective embodimentsof demand gas controllers illustrated in FIGS. 1 and 4, the absence of afluid signal on output leg 70 of the generating means 64 results insupression of the source means 98. Thus, no respirating gas is appliedto the patient during expiration.

When generating means 64 generates the first fluid signal on output leg72 responsive to a sensed positive pressure, the fluid signal is appliedto the apneic event circuit 10 by line 138. The signal travels alongline 138 until it encounters the fluid resistor 140. Resistor 140 blocksthe path of the fluid signal applied on line 138 and causes the fluidsignal to travel around the fluid path 142. The fluid signal travellingaround the path 142 closes the mushroom exhalation valve 130 whichpermits the fluid signal to travel further along to the line 138 andinto the variable capacitance device 132. The fluid signal iscontinuously applied to the variable capacitance device 132 so long asthe generating means 64 is generating the fluid signal.

In normal breathing the generating means 64 will cease generating thefluid signal on output leg 72 long before the variable capacitancedevice 132 is filled to its maximum capacity. In this regard, it isrecalled that the generating means 64 will no longer discharge a fluidsignal on output leg 72 when an inspiration is sensed by the sensingmeans 26. In this case, the patient is breathing satisfactorily andthere is no apneic event.

In abnormal breathing, however, when the patient fails to inspire thegenerating means 64 continues to generate a fluid signal on output leg72. Accordingly, the variable capacitance device 132 continues to expanduntil it is inflated to its maximum capacity. When the variablecapacitance device 132 is inflated to a pressure which expands it to itsmaximum capacity, the fluid pressure builds on line 138 and causes thepower stream entering port 134a of NOR gate 134 to switch from outputport 134c to output port 134d. In this manner, the NOR gate 134 createsa fluid signal on line 144 which is used to activate either singularlyor in combination various signaling means. As shown in FIG. 1, the fluidsignal on line 144 is applied via an intermediate line 148 to apneumatically operated digital counter 136a which is incrementedwhenever the NOR gate 134 switches. Line 144 is also connected to apressure/electric switch 146 which converts the fluid signal on line 144to an electric signal on lines 148 and 150. The electric signal on line148 activates an electrocardiogram (ECG) monitor 136c and the electricsignal on lines 148 and 150 activates an alarm 136b. As mentionedpreviously, the alarm may be either visual, audible or both.

Various sizes and types of elastomeric balloons or other appropriatedevices may be chosen for the variable capacitance device 132. Factorsto be considered in making the choice of which device to use include theelastomeric tension exerted by the device and the maximum fluid-storingcapacity of the device. For example, if it were desired that the apneicevent circuit 10 indicate that the patient has not inspired within a 20second interval, the device 132 should be selected so that it canaccommodate the volume of fluid generated by generating means 64 forthat 20 second period without triggering a switch in NOR gate 134. Ofcourse, should the patient inspire before the variable capacitancedevice 132 reaches its maximum pressurized capacity, the device 132acting in conjunction with the mushroom valve 130 is quickly deflated inthe manner described above.

The display device 158 of the apneic event circuit 10 enables anoperator or attending physician to time the duration of a patient'sexpiration. The display device 158, together with the pressure/electricdevice 152, operate in substantially the same manner as similarcomponents in the counter and display circuits 160 discussed above.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof it will be understood bythose skilled in the art that various alterations in form in detail maybe made therein without departing from the spirit and scope of theinvention. For example, the counter 162 may alternatively be connectedto lines 120 or 102. Moreover, while the invention has been particularlyshown and described with reference to a respirator adapted for clinicaluse (as with a patient for example), it should be understood that theinvention may be used in other fields. For example, the invention may beused in conjunction with gas supply to or apnea detection in a subjectin aeronautical, subteranean or underwater environment.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of supplyingsupplemental dosages of respirating gas to a spontaneously breathing invivo respiratory system having an inspiration period and an expirationperiod, said inspiration period being of duration T₂ during which perioda negative pressure relative to ambient pressure exists in said in vivorespiratory system at the location whereat respirating gas is introducedto said system, said expiration period comprising a positive pressurerelative to ambient pressure existing in said in vivo respiratory systemat the location whereat respirating gas is introduced to said system,said method comprising the steps of:(1) sensing initiation of saidinspiration period; (2) generating a first signal having a durationindicative of the duration T₂ of negative pressure relative to ambientpressure occuring in said in vivo respiratory system during saidinspiration period; (3) using timing means to predetermine a duration T₁for which a dose of respirating gas is to be supplied to said in vivorespiratory system, said duration T₁ being less than the duration T₂ ;(4) generating a second signal having a duration related to the durationT₁ ; (5) using said second signal to control the supplying of gas tosaid respiratory system; (6) supplying immediately in response to saidsensed inspiration a dose of respirating gas to said in vivo respiratorysystem, said dose being supplied only for the duration T₁, said dosebeing supplied substantially at the beginning of said sensedinspiration, said dose of gas being supplied at a rate R₁, said rate R₁being set at a value such that it produces at least as great a rise inthe partial pressure of said gas in blood interfacing with saidrespiratory system as the continuous application of said gas at a lowerrate R₂ for the duration T₂ ; and, (7) automatically repeating steps (1)through (6) for a plurality of successive inspiration periods.
 2. Themethod of claim 1, wherein T₁ is less than 0.25×T₂.
 3. The method ofclaim 1, wherein T₁ is less than 0.5 second.
 4. The method of claim 1,wherein a volume V₁ of gas suplied in said dose is no greater than avolume V₂ of gas produced by the application of said gas at the rate R₂for the duration T₂.
 5. An apparatus for supplying supplemental dosagesof respirating gas to a spontaneously breathing in vivo respiratorysystem having an inspiration period and an expiration period, saidinspiration period being of duration T₂ during which period a negativepressure relative to ambient pressure exists in said in vivo respiratorysystem at the location whereat respirating gas is introduced to saidsystem, said expiration period comprising a positive pressure relativeto ambient pressure existing in said in vivo respiratory system at thelocation whereat respirating gas is introduced to said system, saidapparatus comprising:means for sensing initiation of said inspirationperiod; means for generating a first signal having a duration indicativeof the duration T₂ of negative pressure relative to ambient pressureoccuring in said in vivo respiratory system during said inspirationperiod; timing means connected to said first signal generating means forpredetermining a duration T₁ for which a dose of respirating gas is tobe supplied to said in vivo respiratory system, said duration T₁ beingless than the duration T₂ ; means for generating a second signal havinga duration related to the duration T₁ ; means controlled by said secondsignal for supplying immediately in response to said sensed inspirationa dose of respirating gas to said in vivo respiratory system, said dosebeing supplied only for the duration T₁, said dose being suppliedsubstantially at the beginning of said sensed inspiration, said dose ofgas being supplied at a rate R₁, said rate R₁ being set at a value suchthat it produces at least as great a rise in the partial pressure ofsaid gas in blood interfacing with said respiratory system as thecontinuous application of said gas at a lower rate R₂ for the durationT_(2;) and, means for automatically recycling said apparatus so thatdoses of respirating gas having duration T₁ can be supplied for aplurality of successive inspiration periods.
 6. The apparatus of claim5, wherein T₁ is less than 0.25×T₂.
 7. The apparatus of claim 5, whereinT₁ is less than 0.5 second.
 8. The apparatus of claim 5, wherein avolume V₁ of gas supplied in said dose is no greater than a volume V₂ ofgas produced by the application of said gas at the rate R₂ for theduration T₂.
 9. The apparatus of claim 5, wherein said supply meansprovides gas for a time period corresponding to the duration of saidsecond signal.
 10. The apparatus of claim 9 wherein said first and saidsecond signals are fluidic signals and wherein said means for generatingsaid second signal further comprises:a first output port vented toatmosphere; a second output port fluidically connected to said sourcemeans; a first input port fluidically connected to a power stream, saidfirst input port having a first side and a second side such that saidpower stream is substantially vented to atmosphere through said firstoutput port when the pressures on said first side and said second sideof said first input port are substantially equal; a second input portfluidically connected to said first generating means for receiving saidfirst fluid signal and applying said first fluid signal to said firstside of said first input port, thereby deflecting said power stream fromsaid first output port to said second output port and thereby generatingsaid second fluid signal; and, a fluidic path having a first endconnected to said second input port and on said first side of said firstinput port and a second end connected to said second side of said firstinput port for substantially equalizing the pressure on said first andsaid second sides of said first input port, said fluidic path havingsaid timing means thereon intermediate said first and second endsthereof.
 11. The apparatus of claim 10, wherein said timing means isadapted to control the substantial equilization of pressure on saidfirst and said second sides of said first input port and thus controlthe duration of said second fluid signal.
 12. The apparatus of claim 6wherein said source means provides gas for a time period correspondingto the absence of said second signal at said source means.
 13. Theapparatus of claim 12 wherein said first and second signals are fluidsignals, and wherein said means for generating said second signalfurther comprises:a first output port fluidically connected to saidsource means; a second output port vented to atmosphere; a first inputport fluidically connected to a power stream, said first input porthaving a first side and a second side such that said second generatingmeans generates a second fluid signal out said first output port whenthe pressures on said first side and said second side of said firstinput port are substantially equal; a second input port fluidicallyconnected to said first generating means for receiving said first fluidsignal and applying said first fluid signal to said first side of saidfirst input port, thereby deflecting said power stream from said firstoutput port to said second output port and thereby venting said powerstream to atmosphere; and, a fluidic path having a first end connectedto said second input port and on said first side of said first inputport and a second end connected to said second side of said first inputport for substantially equalizing the pressures on said first and saidsecond sides of said first input port, said fluidic path having saidtiming means thereon intermediate said first and second ends thereof.14. The apparatus of claim 13, wherein said timing means is adapted tocontrol the substantial equilization of pressure on said first and saidsecond sides of said first input port and thus control the duration ofsaid second fluid signal.
 15. A method of supplying supplemental dosagesof respirating gas to a spontaneously breathing in vivo respiratorysystem having an inspiration period and an expiration period, saidinspiration period being of duration T₂ during which period a negativepressure relative to ambient pressure exists in said in vivo respiratorysystem at the location whereat respirating gas is introduced to saidsystem, said expiration period comprising a positive pressure relativeto ambient pressure existing in said in vivo respiratory system at thelocation whereat respirating gas is introduced to said system, saidmethod comprising the steps of:(1) sensing initiation of saidinspiration period; (2) using timing means to predetermine a duration T₁for which a dose of respirating gas is to be supplied to said in vivorespiratory system, said duration T₁ being less than the duration T₂ ofnegative pressure relative to ambient pressure occuring in said in vivorespiratory system during said inspiration period; (3) supplyingimmediately in response to said sensed inspiration a dose of respiratinggas to said in vivo respiratory system, said dose being supplied onlyfor the duration T₁, said dose being supplied substantially at thebeginning of said sensed inspiration, said dose of gas being supplied ata rate R₁, said rate R₁ being set at a value such that it produces atleast as great a rise in the partial pressure of said gas in bloodinterfacing with said respiratory system as the continuous applicationof said gas at a lower rate R₂ for the duration T₂ ; (4) determining theoccurrence of an apneic event if a next expected occurrence of negativepressure created by an inspiration of said in vivo respiratory system isnot sensed within a predetermined time period; and, (5) automaticallyrepeating steps (1), (2), (3), and (4) for a plurality of successiveinspiration periods.
 16. The method of claim 15, wherein T₁ is less than0.25×T₂.
 17. The method of claim 15, wherein T₁ is less than 0.5 second.18. The method of claim 15, wherein a volume V₁ of gas supplied in saiddose is no greater than a volume V₂ of gas produced by the applicationof said gas at the rate R₂ for the duration T₂.
 19. An apparatus forsupplying supplemental dosages of respirating gas to a spontaneouslybreathing in vivo respiratory system having an inspiration period and anexpiration period, said inspiration period being of duration T₂ duringwhich period a negative pressure relative to ambient pressure exists insaid in vivo respiratory system at the location whereat respirating gasis introduced to said system, said expiration period comprising apositive pressure relative to ambient pressure existing in said in vivorespiratory system at the location whereat respirating gas is introducedto said system, said apparatus comprising:means for sensing initiationof said inspiration period; timing means for predetermining a durationT₁ for which a dose of respirating gas is to be supplied to said in vivorespiratory system, said duration T₁ being less than the duration T₂ ofnegative pressure relative to ambient pressure occuring in said in vivorespiratory system during said inspiration period; means for supplyingimmediately in response to said sensed inspiration a dose of respiratinggas to said in vivo respiratory system, said dose being supplied onlyfor the duration T₁, said dose being supplied substantially at thebeginning of said sensed inspiration, said dose of gas being supplied ata rate R₁, said rate R₁ being set at a value such that it produces atleast as great a rise in the partial pressure of said gas in bloodinterfacing with said respiratory system as the continuous applicationof said gas at a lower rate R₂ for the duration T₂ ; means fordetermining the occurrence of an apneic event if said sensing means doesnot sense within a predetermined time period a next occurrence ofnegative pressure created by an inspiration of said in vivo respiratorysystem; and, means for automatically recycling said apparatus so thatdoses of respirating gas having duration T₁ can be supplied for aplurality of successive inspiration periods.
 20. The apparatus of claim19, wherein T₁ is less than 0.25×T₂.
 21. The apparatus of claim 19,wherein T₁ is less than 0.5 second.
 22. The apparatus of claim 18wherein a volume V₁ of gas supplied in said dose is no greater thanvolume V₂ of gas produced by the application of said gas at the rate R₂for the duration T₂.
 23. A method of supplying supplemental dosages ofrespirating gas to a spontaneously breathing in vivo respiratory systemhaving an inspiration period and an expiration period, said inspirationperiod being of duration T₂ during which period a negative pressurerelative to ambient pressure exists in said in vivo respiratory systemat the location whereat respirating gas is introduced to said system,said expiration period comprising a positive pressure relative toambient pressure existing in said in vivo respiratory system at thelocation whereat respirating gas is introduced to said system, saidmethod comprising the steps of:(1) sensing initiation of saidinspiration period; (2) using timing means to predetermine a duration T₁for which a dose of respirating gas is to be supplied to said in vivorespiratory system, said duration T₁ being less than the duration T₂ ofnegative pressure relative to ambient pressure occuring in said in vivorespiratory system during said inspiration period; and, (3) supplyingimmediately in response to said sensed inspiration a dose of respiratinggas to said in vivo respiratory system, said dose being supplied onlyfor the duration T₁, said dose being supplied substantially at thebeginning of said sensed inspiration, said dose of gas being supplied ata rate R₁, said rate R₁ being set at a value such that it produces atleast as great a rise in the partial pressure of said gas in bloodinterfacing with said respiratory system as the continuous applicationof said gas at a lower rate R₂ for the duration T₂ ; and, (4)automatically repeating steps (1), (2), and (3) for a plurality ofsuccessive inspiration periods.